1. Field of the Invention
The invention relates to a process for automatic positioning of a mask relative to a workpiece and a device for executing the process in an exposure device which is used for producing a semiconductor device, a printed board, and a LCD (liquid crystal display) and for similar purposes. The invention relates especially to a process for positioning a mask relative to a workpiece in which the distance between the two alignment marks can be automatically computed; the marks can be used for positioning a mask relative to a workpiece and they are recorded on the workpiece. The invention furthermore relates to a device for executing this process.
2. Description of Related Art
Production of electrical and electronic components and parts of various types in which processing of structures in the micron range is necessary encompasses an exposure process. These electronic parts are semiconductor components, liquid crystal displays, printer heads of the inkjet type, multichip modules in which a plurality of different electronic components are produced on a substrate and thus a module is formed, and the like. In this exposure process, a mask is used in which metal, such as chromium or the like, is vacuum-evaporated and etched on a transparent substrate, such as glass or the like, and a pattern formed. Through this mask, ultraviolet rays are emitted onto the workpiece and the mask pattern is transferred to the photoresist which has been applied to the workpiece.
Exposure systems are divided into the projection printing type, the contact printing type, and the proximity printing system type. In the projection printing type, a mask image is imaged onto the workpiece by a projection lens. In the contact printing system, parallel light is emitted in a state in which the mask and the workpiece are arranged directly abutting one another. In the proximity printing system, parallel light is emitted in a state in which a small intermediate space is formed between the mask and the workpiece.
In this exposure process, it is important in the case of transfer of the mask pattern onto the workpiece, that a pattern to be transferred subsequently is exactly positioned relative to a pattern formed beforehand. The above described positioning is ordinarily done such that the alignment marks of the mask and the workpiece come to rest on top of one another.
FIG. 1 schematically shows the arrangement of a projection exposure device in which the invention can be used. First of all conventional positioning of the mask relative to the workpiece is described below using FIG. 1:
In the figure, an exposure light irradiation device (or a nonexposure light irradiation device) 1, which has a lamp 1a which emits exposure light, for example a high-pressure mercury lamp or the like, a focussing mirror 1b, a shutter 1c, an optical filter 1d which is used when nonexposure light is emitted, and a condenser lens 1e, is shown.
Furthermore, a mask carrier 2 is shown which is driven by means of a drive device (not shown) in the X-Y-Z-.THETA. directions (X-axis, Y-axis: orthogonal axes on a plane parallel to one workpiece carrier surface, Z-axis: an axis perpendicular to the workpiece carrier surface, .THETA.-axis: an axis of rotation around the Z-axis).
Reference letter M designates a mask on which a mask pattern and mask alignment marks MAM1, MAM2 are recorded for purposes of positioning. Reference number 3 indicates a projection lens and reference letter W a workpiece. Workpiece alignment marks WAM1, WAM2 are recorded on workpiece W for purposes of positioning by a workpiece carrier which is driven by a drive (not shown) in the X-Y-Z-.THETA. directions,
Reference number WA1 indicates a workpiece alignment mark partial illumination system. The nonexposure light emitted from a light source (not shown) is incident via optical fibers 6a, furthermore via lens 6b and mirror 6c, on a half mirror 5e of alignment unit 5, and via a lens 5b and a half mirror 5c, irradiates workpiece alignment mark WAM on workpiece W.
An alignment unit 5 consists of a lens 5a, an objective lens 5b, half mirrors 5c and 5e, and an image sensor 5d which has a CCD camera. The mask alignment mark MAM projected onto the workpiece W and the workpiece alignment mark WAM irradiated by workpiece alignment mark partial illumination system WA1 are recorded via half mirror 5c, objective lens 5b, half mirror 5e and lens 5a by means of image sensor 5d.
On each of mask M and workpiece W are several mask alignment marks MAM1, MAM2 and several workpiece alignment marks WAM1, WAM2 (each at two locations in this case), and alignment unit 5 and workpiece alignment mark partial illumination system WA1 are assigned accordingly to the respective alignment mark.
In the figure, mask M is positioned relative to the workpiece W in the following manner:
(1) Workpiece W on which workpiece alignment marks WAM1, WAM2 are recorded is subjected to prealignment and placed on workpiece carrier 4. PA1 (2) Nonexposure light (or exposure light) is emitted from exposure light irradiation device (or a nonexposure light irradiation device) 1 onto mask alignment marks MAM1, MAM2 of mask M. PA1 (3) The images of the above described mask alignment marks, which are imaged on workpiece W, are recorded by image sensors 5d of alignment units 5 and their positions are stored by an image processing device (not shown). Here, it is assumed that the line to the X-axis or Y-axis formed between the above described mask alignment marks MAM1 and MAM2 is set parallel and represents the direction of motion of the workpiece carrier and/or mask carrier. PA1 (4) Nonexposure light (or exposure light) is emitted from workpiece alignment mark partial illumination systems WA1 onto workpiece alignment marks WAM1, WAM2 of workpiece W and workpiece alignment marks WAM1, WAM2 on workpiece W are determined by means of alignment units 5. PA1 (5) Based on the positions of the images of the above described mask alignment marks and the positions of the images of the workpiece alignment marks which were determined by alignment units 5, a measure of the position deviation of mask M from workpiece W is computed. Based on this value, mask carrier 2 and/or workpiece carrier 4 is/are moved and positioning of the mask M relative to the workpiece W is performed. PA1 (1) How many degrees workpiece alignment marks WAM1, WAM2 are angularly offset with reference to mask alignment marks MAM1, MAM2 is computed. This means that how many degrees the segment formed between workpiece alignment marks WAM1 and WAM2 is angularly offset with reference to the segment formed between mask alignment marks MAM1 and MAM2 is computed. (This angular offset is hereinafter called ".DELTA..THETA."). PA1 (2) If the angular offset Ae has been determined in this way, workpiece carrier 4 (or mask carrier 2) is rotated according to angular offset .DELTA..THETA.. PA1 (1) When a mask is positioned relative to a workpiece, by irradiation of the mask alignment marks with exposure light or nonexposure light from a light irradiation part, positioning is performed by determining the images of the mask alignment marks which are imaged on a workpiece, and determining of workpiece alignment marks of the workpiece, and by moving and offsetting the mask and/or the workpiece in two orthogonally intersecting directions parallel to the workpiece surface and rotating the mask and/or workpiece around an axis of rotation which is perpendicular to a plane which contains these two directions, so that the two alignment marks come to rest on top of one another, the workpiece alignment marks located at two locations on the workpiece are each determined and their positions are stored as the first positions. Afterwards the workpiece is rotated by a stipulated first angle. After this rotation, the above described alignment marks located at two locations on the workpiece are each determined again. Their positions are stored as second positions. Based on the data of the above described first and second positions, and as a result of the above described first angle, the distance between the workpiece alignment marks located on the workpiece is determined at two locations. Then, based on the data of the distance between the above described workpiece alignment marks, a second angle is determined which is formed by a line which passes through the workpiece alignment marks at the two locations on the above described workpiece, and by a line which passes through the mask alignment marks at the two locations. According to the above described second angle, the mask or the workpiece is rotated around the above described axis of rotation. After this rotation, the images of the mask alignment marks imaged on the workpiece and the workpiece alignment marks are determined, and the mask and/or workpiece moved such that the two alignment marks come to rest on top of one another. PA1 (2) If the distance between the workpiece alignment marks on the workpiece determined above in (1) is outside a stipulated range, further processes are stopped and an error messages sent.
Computation of the above described measure of the position deviation and the positioning of the mask to the workpiece accomplished thereby are performed in the following manner:
FIG. 8 schematically represents the process for computing the above described measuring of the position deviation. In the figure, the images of the mask alignment marks MAM1, MAM2 and the images of workpiece alignment marks WAM1, WAM2, which were recorded by means of alignment units 5, are shown. In the figure, A and B each identify the images recorded by alignment units 5 located at two positions.
In FIG. 8, the following formula (1) applies when the above described angular offset is are represented as .DELTA..THETA., the respective position coordinates of the workpiece alignment marks WAM1, WAM2 are represented as (x1, y1), (x2, y2) and the distance between them is represented by L: EQU .DELTA..THETA.=sin.sup.-1 ((y2-y1) (1)
The angular offset .DELTA..THETA. can be determined using the above described equation (1) when the position coordinates of the workpiece alignment marks WAM1, WAM2 are found, since the distance L is stipulated.
After rotation, again, mask alignment marks MAM1, MAM2 and workpiece alignment marks WAM1, WAM2 are determined by means of alignment units 5. Workpiece carrier 4 and/or mask to carrier 2 is/are moved in the X-axis direction and/or Y-axis direction such that two alignment marks MAM1, WAM1 and MAM2, WAM2 come to rest on top of one another.
After positioning of mask M to workpiece W in the above described manner, exposure light is emitted from exposure light irradiation device (or nonexposure light irradiation device) 1, the mask pattern is projected on workpiece W, and exposure is accomplished.
The distance L between workpiece alignment marks WAM1 and WAM2 on the workpiece does change according to the size of workpiece W. But, it is a value that is specific to the manufacturer. Distance L was therefore conventionally integrated in the computer run in the process of producing the exposure device.
Furthermore, under certain circumstances there was additionally a means for distinguishing the size of workpiece W, different values of L were stored in the device and a value of L which corresponds to the size of workpiece W was called up.
However, workpiece alignment marks WAM are often located in the strips between the circuit patterns and in the peripheral area of the workpiece in which a circuit pattern cannot be formed. Recently, therefore, there have been workpieces with different distances L between workpiece alignment marks WAM1 and WAM2 as a result of the different types (shape, size) of circuit patterns produced in the workpiece, even if they originate from the same manufacturer and have the same size. It has, therefore, become more and more difficult to integrate the value of L beforehand in the exposure device as a constant.
To handle products with different distances L between workpiece alignment marks WAM1 and WAM2, therefore, the value of L must be manually set; this causes more working steps. Furthermore, here, there is the danger that adjustment errors are caused when the value of the above described distance L is set.